I've always wondered as to the actual mechanics of how partisan-sponsored polls generate more favorable numbers for their own candidates - especially since they are able to do it with such consistency! Is it due to unintended, but overly optimistic assumptions? Is it due to wording the questions in an intentionally leading way? Is it due to selectively using more favorable demographics when choosing sample type, size, and polling timeframe? Is it due to after-the-fact manipulation of the numbers? All of the above? Something else?